1. Field of the Invention
The present invention relates to an image processing method and image processing apparatus that process data for performing printing using ink, and to an inkjet printing method that performs printing using ink.
2. Description of the Related Art
In inkjet printing, the capability to form high-quality images on various kinds of printing media is strongly desired. Particularly, in recent years, photo quality is desired, and glossy paper capable of achieving the same image quality and texture as silver halide photos is widely available in the market. Moreover, together with the increasing demand for image quality, there is also a demand for the same resistance to weather as silver halide photos, and as measures for achieving that, inkjet printers that use pigment ink having high robustness of the coloring material itself are increasing.
As one problem with inkjet printers that use this kind of pigment ink is a bronzing phenomenon that occurs due to discoloration of regular reflected light. This bronzing phenomenon is a phenomenon that occurs as a result of the ratio of the wavelength component of the absorption band of pigment in reflected light becoming large due to selective reflection on the pigment particle surface when particles of pigment coloring material are exposed on the surface of the printing medium. Particularly, when using cyan pigment, reflected light causes a reddish color to occur, and causes the visual quality of the image to be greatly degraded.
As one method to reduce the bronzing phenomenon is a method of laminating a transparent film over the printed surface so that the pigment particles are not exposed on the surface of the printing medium. However, there are various problems with this method in that having a mechanism for that kind of lamination increases the cost of the printing apparatus, and the lamination work itself takes a lot of time.
As another technique is a technique disclosed in Japanese Patent Publication No. 4,066,338 of overcoating a printing medium with yellow ink. More specifically, after an image is formed on a printing medium using cyan, magenta and yellow ink, overcoating is performed at a printing rate of 10% or less using a yellow ink for which the bronzing phenomenon does not easily occur, which suppresses the bronzing phenomenon in especially the cyan hue.
Incidentally, in the technique disclosed in Japanese Patent Publication No. 4,066,338, there is a problem in that as the color changes due to overcoating of yellowing ink, color reproducibility is affected. Particularly, change of gray colors which are severe to the color change upsets the gray balance, and the degradation of image quality becomes even worse. In recent years, the printing monochrome photos with an inkjet printer is also increasing, and inkjet printers having a special printing mode for printing monochrome photos are being sold. In a special monochrome photo mode, the gray balance is the most important item related to image quality, and when the method of overcoating using yellow ink as disclosed in Japanese Patent Publication No. 4,066,338 is used, the effect on color reproducibility is especially large.